1. Field of the Invention
The present invention relates to controllers and controlled devices constituting a semiconductor manufacturing apparatus.
2. Description of the Related Art
In the production of semiconductor wafers, some unpredictable problems may occur. One such problem is the halting of a controller of a semiconductor manufacturing apparatus. Recently, conventional inexpensive personal computers (PCs) have been used as controllers. However, each component of PCs, hard disk for instance, has its own lifespan, and it cannot be used indefinitely without faults causing stoppage.
To avoid problems caused from stoppage of PC components as mentioned above, a method of detecting the stoppage of a controller using a hardware timer circuit called Watch Dog Timer (WDT) is known. This WDT is used to monitor a state of controlling program running at a controller and to detect abnormal execution of the program. A monitored program sends a reset signal to a WDT at a constant cycle. The monitored program stops outputting the reset signal when the monitored program is under a state of abnormal execution. If the WDT has not received the reset signal for a certain period of time, the WDT sends a command to stop the monitored program.
Jpn. Pat. Appln. KOKAI Publication No. H5-81080 discloses a technique of implementing the WDT function by software instead of modifying hardware structure on a microprocessor-failure monitoring apparatus so that states of a program on a microprocessor can be monitored and errors can be detected by software without causing an extra complication in hardware structure.
When a failure occurs at a controller, depending on the timing of the failure, states of devices may not be monitored, anomalies of devices may not be detected by the controller, and thus, the devices may not be terminated and this situation risks harm to equipment. For instance, if a pressure controller fails, a gas may continue flowing into a wafer processing chamber, and pressure in the processing chamber may keep increasing. Continuing operation of device functions without termination during the controller's malfunctioning may cause a serious danger not only to the semiconductor manufacturing apparatus itself, but to workers around the apparatus.
If an interface board breaks down, the program on the interface board cannot receive commands from the controller, and similarly, the uncontrolled devices may cause a dangerous situation as well.